The University of Georgia, Department of Biochemistry, Life Science Building, Athens, Georgia 30602.
Plant Physiol. 1992 Mar;98(3):1163-9. doi: 10.1104/pp.98.3.1163.
Here it is reported that sucrose synthase can be readily measured in growing wild tomato fruits (Lycopersicon chmielewskii) when suitable methods are adopted during fruit extraction. The enzyme also was present in fruit pericarp tissues, in seeds, and in flowers. To check for novel characteristics, the wild tomato fruit sucrose synthase was purified, by (NH(4))(2)SO(4) fraction and chromatography with DE-32, Sephadex G-200, and PBA-60, to one major band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The following characteristics were obtained: native protein relative molecular weight 380,000; subunit relative molecular weight 89,000; K(m) values with: sucrose 53 millimolar, UDP 18.9 micromolar, UDP-glucose 88 micromolar, fructose 8.4 millimolar; pH optima between 6.2 to 7.3 for sucrose breakdown and 7 to 9 for synthesis; and temperature optima near 50 degrees C. The enzyme exhibited a high affinity and a preference for uridylates. The enzyme showed more sensitivity to divalent cations in the synthesis of sucrose than in its breakdown. Sink strength in tomato fruits also was investigated in regard to sucrose breakdown enzyme activities versus fruit weight gain. Sucrose synthase activity was consistently related to increases in fruit weight (sink strength) in both wild and commercial tomatoes. Acid and neutral invertases were not, because the published invertase activity values were too variable for quantitative analyses regarding the roles of invertases in tomato fruit development. In rapidly growing fruits of both wild and commercially developed tomato plants, the activity of sucrose synthase per growing fruit, i.e. sucrose synthase peak activity X fruit size, was linearly related to final fruit size; and the activity exceeded fruit growth and carbon import rates by at least 10-fold. In mature, nongrowing fruits, sucrose synthase activities approached nil values. Therefore, sucrose synthase can serve as an indicator of sink strength in growing tomato fruits.
这里报道了在采用适当的提取方法时，蔗糖合酶可以在生长中的野生番茄果实（Lycopersicon chmielewskii）中轻易地被测量。该酶也存在于果实的果皮组织、种子和花朵中。为了检查新的特性，野生番茄果实蔗糖合酶通过（NH4）2SO4分级和用 DE-32、Sephadex G-200 和 PBA-60 进行的层析被纯化，在十二烷基硫酸钠-聚丙烯酰胺凝胶电泳上出现一条主要的带。得到以下特性：天然蛋白质的相对分子量为 380000；亚基的相对分子量为 89000；与以下物质的 Km值：蔗糖 53 毫摩尔，UDP 18.9 微摩尔，UDP-葡萄糖 88 微摩尔，果糖 8.4 毫摩尔；蔗糖分解的最适 pH 值在 6.2 到 7.3 之间，合成的最适 pH 值在 7 到 9 之间；最适温度接近 50°C。该酶对尿苷酸具有高亲和力和偏好性。与蔗糖分解相比，该酶在合成蔗糖时对二价阳离子更敏感。在番茄果实中还研究了蔗糖分解酶活性与果实增重之间的关系，以了解果实的库强。蔗糖合酶活性与野生和商业番茄果实的增重（库强）呈一致的相关关系。酸和中性转化酶则不然，因为已发表的转化酶活性值变化太大，无法对转化酶在番茄果实发育中的作用进行定量分析。在野生和商业开发的番茄植株的快速生长的果实中，每生长一个果实的蔗糖合酶活性，即蔗糖合酶峰值活性×果实大小，与最终果实大小呈线性关系；而且该活性超过了果实生长和碳输入率至少 10 倍。在成熟的非生长果实中，蔗糖合酶活性接近零值。因此，蔗糖合酶可以作为生长中的番茄果实库强的指标。
